Field of the Invention
The invention relates to a coupling device for connecting an optical fiber to an optical transmitting or receiving unit and transmitting or receiving device having a coupling device. More specifically, the invention relates to a coupling device for coupling an optical fiber to an optical transmitting or receiving unit, in particular a laser diode. The coupling device has a main section with an accommodation opening to accommodate an optical fiber, and a section projecting like a step and having a flattened surface for fixing the transmitting or receiving unit. In addition, the invention relates to a transmitting or receiving unit having such a coupling device.
Janssen (U.S. Pat. No. 4,874,217) discloses a device for coupling a laser chip to an optical fiber. In this case, a hollow cylinder is adjoined by a semi-cylindrical projection that is fixed to it and on whose flattened side there is a plate-like platform to accommodate the laser chip. The optical fiber, whose end section is constructed as a taper, is disposed in a continuous opening in the long side of the hollow cylinder. The hollow cylinder has longitudinal and transverse incisions in the area of the projection, in order to make the latter deformable for adjusting the laser chip. The hollow cylinder and a further external sleeve of the hollow cylinder are made of metal, and the plate-like platform is produced substantially from diamond.
The drawbacks with the known device are a complex construction and the requirement for active adjustment, which is accomplished by deforming the semi-cylindrical projection. Because of the use of a taper at the end of the fiber, the active adjustment has to be conducted in this case with low tolerance. Adjustment errors in the light propagation direction on the order of magnitude of one micrometer (1 xcexcm) already have the effect of considerable coupling losses in optical fibers having a taper. Separate positioning elements that contribute further to a complicated construction of the known device are necessary for the deformation of the semi-cylindrical projection necessary for the adjustment and for the fixing of an optimum adjustment.
It is accordingly an object of the invention to provide a coupling device for connecting an optical fiber to an optical transmitting or receiving unit and transmitting or receiving device having a coupling device that overcome the herein-aforementioned disadvantages of the heretofore-known devices of this general type by coupling an optical fiber to a transmitting or receiving unit with a simple construction while being produced cost-effectively and with reduced effort.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a coupling device for coupling an optical fiber to an optical transmitting or receiving unit. The coupling device includes a main section with an accommodation opening for accommodating an optical fiber. A section is formed in one piece with the main section from nonconductive material, projects like a step, and has a flattened surface for directly mounting the transmitting or receiving unit. The optical transmitting or receiving unit projects like a step or a contact-making surface applied to the flattened surface. The flattened surface of the section projects like a step having a longitudinal notch for positioning the transmitting or receiving unit.
Consequently, according to the invention, a single-piece coupling device is provided which includes an electrically insulating material and in which the optical transmitting or receiving unit can be mounted directly on a portion projecting like a step or a contact-making surface applied to the latter.
The elements to be connected with an optical coupling are therefore mounted directly on a single-piece component. Separate components or additional electrical insulators can be omitted. The outlay on material and the overall size of the device are reduced considerably as compared with the prior art.
In addition, the flattened surface of the section projecting like a step has, according to the invention, a longitudinal notch, which is used for positioning the transmitting or receiving unit. The longitudinal notch passively aligns the transmitting or receiving element. Corresponding structures belonging to a transmitting or receiving element engage the longitudinal notch. Appropriate structuring is accomplished, for example, by etching, by grinding or by laser machining.
The passive alignment and centering of the transmitting and receiving component dispenses with the requirement for active adjustment transversely with respect to the longitudinal axis of the device. The transmitting or receiving element to be mounted is positioned automatically when it is placed on the projecting section.
In a preferred embodiment, the flattened surface of the section projecting like a step is located in a plane that intersects the extension of the accommodating opening in the main section. The longitudinal notch represents the continuation of the accommodation opening in the projecting section. The longitudinal axis is therefore produced automatically during the production of the device: it is the remaining part of the continuous accommodation opening in the main section. The material present above the (subsequently) projecting section is removed during the production. In this configuration, the longitudinal notch is produced in a very effective way by using structures that are already present.
In this embodiment, the flattened surface of the section projecting like a step merely must lie in one plane that intersects the extension of the accommodation opening of the main section. In this case, provision may be made for the accommodation opening to be intersected above or below its center. Depending on this, the longitudinal notch has a different width and depth.
In one embodiment, the accommodation opening is intersected not quite at its center, so that the axis of an optical fiber guided in the accommodation opening does not lie in the plane of the surface of the projecting section, which could make coupling light into or out of the optical fiber more difficult, depending on the construction.
In a preferred configuration, the section projecting like a step adjoins the main section rigidly, that is to say substantially without incisions or cutouts. The rigid connection of the section projecting like a step to the main section has the advantage that, after the transmitting or receiving unit has been fixed to the projecting section, there is defined positioning with respect to an optical fiber to be coupled on.
The step-like section preferably forms a vertical stop for the transmitting or receiving element. Positioning in the z-direction as it is placed on the step-like area therefore takes place directly via the surface formed by the step-like section.
In a preferred development of the invention, the section projecting like a step has a structured metallization. The metallization is here structured in as much as only specific structured areas are provided with a metallization, rather than the entire area of the step-like section. In particular, the structured metallization encompasses conductor tracks for making contact with the transmitting or receiving element. The structured metallization is used in particular to make electrical contact with the transmitting or receiving unit. However, it can likewise be used for fixing the transmitting or receiving unit on the projecting section, for example by soldering or bonding.
In a development of the invention, the area projecting like a step has depressions to accommodate fixers and/or contact-makers for the transmitting or receiving element. These depressions are produced, for example, by grinding or milling the projecting section. They mechanically fix the transmitting or receiving unit independently of the step of positioning the transmitting or receiving element.
In this case, for example, a material that performs the joining or fixing of the correctly positioned transmitting or receiving element is introduced into the corresponding depressions.
Furthermore, the depressions can, at least partially, also have contact-makers such as a structured metallization. The fixing of the transmitting or receiving element can in this case, and also in making electrical contact, for example be carried out within the context of using a conductive adhesive or by soldering and adhesive bonding. Reference is made to the fact that any desired types of fixing the transmitting or receiving element are possible.
In an advantageous refinement, a monitor diode can be mounted on the section projecting like a step, in addition to the transmitting or receiving unit. The monitor diode is likewise placed directly on the projecting section or a metallization located on the latter. If necessary, depressions can be provided in the projecting section, said projections bringing the monitor diode into a sunken position and aligning it passively in a desired position. In this case, a preferred exemplary embodiment provides for the optically active face of the monitor diode to point upward. Light to be detected is in this case diffracted in the direction of the optically active face via a bevel.
The accommodation opening for the optical fiber preferably extends through the main section as a continuous longitudinal opening. The end section to be coupled of the optical fiber terminates substantially with the end of the accommodation opening facing the projecting section. In this case, the end of the optical fiber preferably projects from the accommodation opening by a defined distance. This is expedient, for example from the point of view that the edge running between the projecting section and the main section may possibly have a certain rounding, so that it is not possible to position the transmitting or receiving unit directly at the accommodation opening. Otherwise, more defined positioning of the optical fiber is possible if it projects from the accommodation opening by a defined distance.
The coupling device is preferably constructed as a hollow ceramic cylinder. This simplifies the production considerably. Such a ceramic cylinder is a conventional, prefabricated high-precision component and is also used for other purposes. By removing part of the cylinder, it is adapted to be used as a coupling device. In order to form a cylindrical projection, the ceramic cylinder is either ground suitably or undergoes laser machining, in which the removal of material is accomplished in a suitable way.
In one preferred embodiment, the size and shape of the ceramic cylinder corresponds to a normal ferrule for standard optical fiber plugs, as are used in optical communications technology. The further use of the device, for example coupling to an optical plug via a slit sleeve, is simplified considerably, since standard components can be used.
The portion of the coupling device that projects like a step preferably has a semi-cylindrical shape. During the production of the device, it is therefore merely necessary for that part of the cylinder that is located above this section to be removed. This can be done in one operation. The flattened side is in this case produced automatically.
The transmitting or receiving unit according to the invention has an optical transmitting or receiving unit, an optical fiber, and a coupling device having a portion projecting like a step. It permits the coupling of a transmitting or receiving unit, in particular a laser diode, to an optical fiber in a simple way.
In this case, the transmitting or receiving unit preferably has contours on its surface that interact with corresponding contours. That is to say, the longitudinal notch in the section projecting like a step in order to align the transmitting and receiving unit passively. Therefore, no active adjustment of the position of the transmitting or receiving element is required, instead passive positioning of the component is accomplished.
In a preferred embodiment, the optical fiber is disposed at a distance from the transmitting or receiving unit, the optical fiber projecting from the accommodation opening by a defined distance. Optical coupling is preferably completed in this case via an optically transparent, index-matched casting compound. The index-matched casting compound in this case reduces the occurrence of reflections at the end face of the optical fiber. In addition, it provides protection for the configuration against environmental influences.
The end section of the optical fiber adjoining the transmitting or receiving unit is preferably blunt. In this way, it can rest with the entire cross-sectional area on the unit. This configuration can be produced in a straightforward manner, and the coupling losses are kept low.
The transmitting or receiving unit is preferably mounted on the flattened side of the projecting section. In this case, the unit can be positioned easily. The transmitting and receiving unit preferably rests on the edge between the cylindrical section and the projecting section. The edge provides a reference line, which permits simple mounting.
When a laser diode is used as the transmitting or receiving unit, this is preferably rotated through 180xc2x0 and mounted on the projecting section with the chip surface downward. As a result, the sensitivity with respect to tolerance deviations between the laser channel and the wave guide channel is reduced, since the influence of the chip thickness tolerance is minimized.
The laser diode is preferably constructed as a tapered laser diode, that is to say taper elements are integrated into the laser chip. For this reason, additional taper elements outside the chip, between the laser diode and optical fiber, are dispensed. The use of a tapered laser diode in conjunction with a wave guide end which is butt-coupled permits relatively high tolerance deviations in the alignment of the laser channel and wave guide channel, so that passive alignment of the laser diode on the projecting section of the coupling device is possible without the requirement for active adjustment.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a coupling device for connecting an optical fiber to an optical transmitting or receiving unit and transmitting or receiving device having a coupling device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.